1. Field of the Invention
The present invention relates to a method of producing fine powders, such as a Sn powder, Pb powder, Zn powder, Ni powder, In powder, Sb powder, Cd powder, As powder, Pb--Sb--Sn powder, Pb--Sb--As powder, Re powder, Mo powder, Se powder, Te powder, Cu powder, CdS powder etc.
Sn powder is used as a soldering material or a sensor material. Pb powder is used as a soldering material, a pigment material for paints, a molding material, a sintering material or a cell material. Zn powder is used as a rust-proof material or a cell material. Ni powder is used as an electrode paste material, or an electrode material of a battery and a fuel cell. In powder is used as a soldering material, a sintering material or a dental material. Sb powder is used as a resistive material or a sensor material. Cd powder is used as a catalyst, a powder metallurgy material, in preparation of various ceramic materials or a Ni--Cd battery material. As powder is used as a sensor material. Pb--Sb--Sn powder and Pb--Sb--As powder are used as a cell material. Re powder is used as a filament material or a catalyst. Mo powder is used as a powder metallurgy material or an electron tube material. Se powder is used as an optical semiconductor or a catalyst. CdS powder is used as a solar cell material.
2. Description of the Prior Art
As conventional methods of producing fine powders, a mechanical pulverizing method, an electrolytic method, a spraying method, a volatilization cohesion method or a reduction method are employed.
As mechanical pulverizing methods, a stamp mill method, a ball-mill method and a whirl mill method are used. As electrolytic methods a wet electrolytic method and a dry electrolytic method are used. Furthermore, as spraying methods, a gas spraying method and a water spraying method are used.
The volatilization cohesion method is used in producing the Zn powder. As reduction methods, there are a high temperature reduction method and a salt solution reduction method. The high temperature reduction method is a method for reducing metal compounds with a reducing gas at high temperatures. As the salt reduction method, there are such methods as introducing the metal powder into a metal salt solution to obtain the fine powder by displacement deposition, a reduction method by hydrazine and the like and a reduction method by sodium hypophosphite and DMAB.
In the mechanical pulverizing method, a resultant powder is scaly with a low bulk density. There is also a possibility of mingling of impurities due to wear of a pulverizer and other causes. Moreover, the powder is susceptive to oxidation while the metal and alloy are pulverized. This method is also liable for a cause of dust pollution.
In the electrolytic method, the cost of plant and equipment is apt to increase, and besides, the powder is susceptive to oxidation.
In the spraying method, a grain diameter of the powder is tens of micron and the cost of plant and equipment is high.
The volatilization cohesion method, is limited to production of metal powders having a high vapor pressure such as Zn.
In the high temperature reduction method, the grain diameter of the resultant powder is large and impurities are apt to mingle.
In a displacement deposition method, the metal powder added for effecting displacement deposition is expensive and there is a possibility of impurities to mingle. Moreover, there is inconvenience in handling for depositing the powder.
In a method of precipitating the powder by using such reducing agents as hydrazine, sodium hypophosphite, DMAB and so on, the metals to be reduced are limited and there is a possibility that phosphorus and boron may mingle into the resultant powder as impurities.